Bonding tools for bonding machines, bonding machines for bonding semiconductor elements, and related methods

ABSTRACT

A bonding tool for bonding a semiconductor element to a substrate on a bonding machine is provided. The bonding tool includes a body portion including a contact region for contacting the semiconductor element during a bonding process on the bonding machine. The bonding tool also includes a standoff extending from the body portion, and configured to contact the substrate during at least a portion of the bonding process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 16/248,312 filed on Jan. 15, 2019, which claims the benefit ofU.S. Provisional Application No. 62/621,199 filed on Jan. 24, 2018, thecontents of both of which are incorporated herein by reference.

FIELD

The present invention relates to the formation of semiconductorpackages, and more particularly, to improved bonding tools for use inconnection with bonding machines for bonding semiconductor elements.

BACKGROUND

In certain aspects of the semiconductor packaging industry,semiconductor elements are bonded to bonding locations. For example, inconventional die attach (also known as die bonding) applications, asemiconductor die is bonded to a bonding location of a substrate (e.g.,a leadframe, another die in stacked die applications, a spacer, etc.).In advanced packaging applications, semiconductor elements (e.g., baresemiconductor die, packaged semiconductor die, etc.) are bonded tobonding locations of a substrate (e.g., a leadframe, a PCB, a carrier, asemiconductor wafer, a BGA substrate, another semiconductor element,etc.), with conductive structures (e.g., conductive bumps, contact pads,solder bumps, conductive pillars, copper pillars, etc.) providingelectrical interconnection between the semiconductor element and thesubstrate.

In certain applications of thermocompression bonding, a material (e.g.,an underfill material) is applied in the area between the semiconductorelement and the substrate after the thermocompression bonding operationis complete. Unfortunately, this area may vary (e.g., in terms ofvolume, for example, because of device variations (e.g., variations inthe thickness of a solder mask layer on the substrate)).

Thus, it would be desirable to provide improved bonding tools, bondingmachines including such bonding tools, and related methods.

SUMMARY

According to an exemplary embodiment of the invention, a bonding toolfor bonding a semiconductor element to a substrate on a bonding machineis provided. The bonding tool includes a body portion including acontact region for contacting the semiconductor element during a bondingprocess on the bonding machine. The bonding tool also includes astandoff extending from the body portion, and configured to contact thesubstrate during at least a portion of the bonding process.

According to another exemplary embodiment of the invention, a bondingmachine for bonding a semiconductor element to a substrate is provided.The bonding machine includes a bonding tool. The bonding tool includes(a) a body portion including a contact region for contacting thesemiconductor element during a bonding process on the bonding machine,and (b) a standoff extending from the body portion, the standoff beingconfigured to contact the substrate during at least a portion of abonding operation. The bonding machine also includes a support structurefor supporting the substrate.

According to yet another exemplary embodiment of the invention, a methodof operating a bonding machine is provided. The method includes: (a)carrying a semiconductor element with a bonding tool; (b) initiatingcontact between conductive structures of the semiconductor element withcorresponding conductive structures of a substrate; (c) lowering thebonding tool after step (b) such that a standoff of the bonding toolcontacts an upper surface of the substrate; and (d) raising the bondingtool after step (c).

According to yet another exemplary embodiment of the invention, a methodof operating a bonding machine is provided. The method includes: (a)carrying a semiconductor element with a bonding tool; (b) initiatingcontact between the semiconductor element and an adhesive material on asubstrate; and (c) lowering the bonding tool after step (b) such that astandoff of the bonding tool contacts an upper surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIG. 1 is a block diagram side view of a bonding machine in accordancewith an exemplary embodiment of the invention;

FIG. 2 is a block diagram side view of another bonding machine inaccordance with an exemplary embodiment of the invention;

FIGS. 3A-3E are block diagram side views of elements of the bondingmachine of FIG. 1 illustrating a method of operating the bonding machinein accordance with an exemplary embodiment of the invention; and

FIGS. 4A-4B are block diagram side views of elements of a die attachmachine illustrating a method of operating the bonding machine inaccordance with an exemplary embodiment of the invention.

DETAILED DESCRIPTION

As used herein, the term “semiconductor element” is intended to refer toany structure including (or configured to include at a later step) asemiconductor chip or die. Exemplary semiconductor elements include abare semiconductor die, a semiconductor die on a substrate (e.g., aleadframe, a PCB, a carrier, a semiconductor chip, a semiconductorwafer, a BGA substrate, a semiconductor element, etc.), a packagedsemiconductor device, a flip chip semiconductor device, a die embeddedin a substrate, a stack of semiconductor die, amongst others. Further,the semiconductor element may include an element configured to be bondedor otherwise included in a semiconductor package (e.g., a spacer to bebonded in a stacked die configuration, a substrate, etc.).

As used herein, the term “substrate” is intended to refer to anystructure to which a semiconductor element may be bonded (e.g.,thermocompressively bonded, ultrasonically bonded, thermosonicallybonded, die bonded, etc.). Exemplary substrates include, for example, aleadframe, a PCB, a carrier, a semiconductor chip, a semiconductorwafer, a BGA substrate, a semiconductor element, etc. In accordance withcertain exemplary aspects of the invention, a standoff (included in abonding tool) may contact the substrate during at least a portion of abonding process: it is understood that the standoff (or any extension ofthe standoff) may contact any part of the substrate (or any extension ofthe substrate).

In accordance with exemplary aspects of the invention, a bonding tool(e.g., a placer tool) is provided for a bonding machine, such as athermocompression bonder (TCB) machine, a flip chip bonding machine,etc. For example, such a bonding tool may be attached to, orincorporated with, a heater (e.g., a pulse heater) for heating asemiconductor element in connection with a thermocompression bondingoperation. In other embodiments of the invention, a bonding tool isprovided for a die attach machine or other bonding machine.

In connection with a thermocompression bonding process, the bonding toolplaces a semiconductor element (e.g., a semiconductor die, aninterposer, etc.) on, and bonds the semiconductor element to, asubstrate (e.g., a semiconductor chip, a wafer, etc.). The substrateconfigured to receive the semiconductor element provides mechanicalsupport for the semiconductor element, but may also provide electricalconnection to the semiconductor element (through correspondingconductive structures on each of the substrate and the semiconductorelement). For example, flip chip bonding of the semiconductor element tothe substrate may include by in-situ melting and re-solidifying solderbumps on the semiconductor element being placed. In a specific example,the conductive structures on the substrate may be formed, for example,by etching copper sheets laminated onto a non-conductive material.

Often, the substrate includes a solder mask layer on top with openingsto constraint the solder location during the solder joint formation. Inpractice, the solder mask layer thickness varies from location tolocation on the same substrate, and from batch to batch in differentproduction lots. After thermocompression bonding of the semiconductorelement(s) to the substrate, the now bonded substrate may go through acleaning process and an encapsulation compound molding process.

In connection with the operation of certain bonding machines (e.g., flipchip bonding machines, TCB machines, etc.), a “standoff height” may bedefined. For example, the standoff height (SOH) may refer to thedistance between (a) the top surface of the semiconductor element beingbonded and (b) the upper surface of the substrate (which may be theupper surface of the solder mask layer, in embodiments where thesubstrate includes a solder mask layer). FIG. 1 provides an exemplaryillustration of a standoff height. The consistency of the standoffheight (SOH) may significantly impact the molding consistency.Unfortunately, the standoff height may be difficult to maintain fromdevice to device, at least in part, because of varying solder maskthickness on the substrate.

Aspects of the invention relate to bonding/placement tools (and relatedbonding machines), and methods of operating bonding machines, tocompensate for issues such as solder mask variation, thereby providing amore consistent standoff height. In specific examples of the invention,the bonding/placement tools include one or more standoffs (e.g.,extending from the contact surface of the tool) which may be used todetect the solder mask layer during thermocompression bonding. Usingsuch an approach, the final distance from the semiconductor element tothe upper surface of the substrate (e.g., the standoff height) may bemade more consistent.

The “standoff” provided on the bonding/placement tool may be, forexample, a post, a plurality of posts, a wall, a plurality of walls,among other structures.

The bonding tool may be a heated tool where the heater and the tool areintegrated into one component. In other examples, a heater separate fromthe bonding tool may be provided. In yet other examples, non-heatedbonding tools may be utilized. Bonding tools according to the inventionmay define one or more vacuum paths that provide vacuum used to hold thesemiconductor elements.

Bonding tools according to the invention may be used in connection witha bonding machine (e.g., a thermocompression bonding machine (TCBmachine), a flip chip bonding machine, a conventional die attachmachine, etc.). In connection with a thermocompression bonding machine,the bonding tool may refer to a part that can be attached onto, orintegrated with, the pulse heater (in an embodiment where the heater isseparate from the tool). The bonding tool may sometimes be referred toas a collet, a die collet, a placer tool, a placement tool, among othernames, depending on the application.

In a TCB process, the bonding tool typically places and bonds asemiconductor element (e.g., a die or interposer) to a substrate (e.g.,any type of substrate such as a chip, a wafer, etc.) by in-situ meltingand re-solidifying solder bumps on the semiconductor element beingplaced. Heat is typically applied from the semiconductor element sideonly, while the substrate is typically maintained at a low stagetemperature, as opposed to isothermal heating in mass reflow.

Throughout the various drawings, like reference numerals refer to thelike elements.

Referring now to the drawings, FIG. 1 illustrates bonding machine 100(e.g., a thermocompression bonding machine, a flip chip bonding machine,etc.). Bonding machine 100 includes bond head assembly 102 carrying abonding tool 102 a. Bonding tool 102 a may be formed, for example, usinga high heat conductivity material such as an aluminum nitride ceramicmaterial. Of course, other materials are contemplated for bonding tool102 a (and other tools within the scope of the invention). Bonding tool102 a includes a body portion 102 a 1 carrying (e.g., using vacuum,etc.) semiconductor element 104. Bonding tool 102 a includes a contactsurface 102 a 2 for contacting semiconductor element 104 during abonding process. Bonding tool 102 a also includes standoff 102 a 3(e.g., a post or the like). Semiconductor element 104 includesconductive structures 104 a (e.g., Sn contacts configured for solderinterconnection).

Bonding machine 100 also includes a support structure 108 (e.g., a chuckor the like) (where support structure 108 is carried by machine base110). Substrate 106 is supported by support structure 108, and includesconductive structures 106 b configured for connection (e.g., solderinterconnection) to respective conductive structures 104 a. Solder masklayer 106 a is provided on an upper surface of substrate 106. Thestandoff height (SOH) is shown as the distance/height between an uppersurface of semiconductor element 104 and the upper surface of soldermask layer 106 a (of course, in FIG. 1 the SOH is shown withsemiconductor element 104 above, and not bonded to, substrate 106—andthe SOH may also measured in the bonded position as shown in FIG. 3E).

FIG. 2 illustrates a bonding machine 100′ that is very similar tobonding machine 100 from FIG. 1. As between FIG. 1 and FIG. 2, likereference numbers refer to the same (or similar) elements. As comparedto bonding tool 102 a (shown in FIG. 1, which includes a single standoff102 a 3), bonding tool 102 a′ (included in bonding head assembly 102′ ofbonding machine 100′ in FIG. 2) includes a plurality of standoffs 102 a3 (in the example shown in FIG. 2, two standoffs 102 a 3 are provided).Any number of standoffs may be provided, as desired in the givenapplication. Further, the standoffs may have any desired configurationsuch as a post, a wall, etc. Such variations (e.g., the number ofstandoffs, the types of standoffs such as post or wall, etc.) may beapplicable to any application of the invention including but not limitedto flip chip bonding, thermocompression bonding, and die attachprocesses.

FIGS. 3A-3E illustrate a bonding operation of bonding machine 100 ofFIG. 1 (with certain elements removed for simplicity), with a singlestandoff 102 a 3, but is also applicable to embodiments with multiplestandoffs 102 a 3 (such as shown in FIG. 2). At FIG. 3A, bonding tool102 is moving toward, and approaching substrate 106 (as illustrated bythe downward arrow). FIG. 3B illustrates initial contact between (i)conductive structures 104 a of semiconductor element 104 and (ii)corresponding conductive structures 106 b of substrate 106. This initialcontact may be detected (and/or declared) using any of a number ofmethods such as bond force detection (e.g., a change in bond force),position detection (e.g., using a z-axis position measurement/detectionsystem), velocity detection, among other techniques. FIG. 3C illustratessolder melting, etc. such that pairs of conductive structures 104 a/106b have begun to change form. At FIG. 3D, standoff 102 a 3 has madecontact with solder mask layer 106 a of substrate 106. This contact maybe detected (and/or declared) using any of a number of methods such asbond force detection (e.g., a change in bond force), position detection(e.g., using a z-axis position measurement/detection system), velocitydetection, among other techniques. After this contact is detected,bonding tool 102 a may be raised a predetermined distance (such that a“final” SOH is established, see FIG. 3E), and then the pairs of modified(e.g., melted) conductive structures 104 a/106 b will solidify in thisposition. Following FIG. 3E, underfill material may be added in the gapbetween semiconductor element 104 and substrate 106, followed byencapsulation.

Aspects of the invention are also applicable to die attach tools, dieattach equipment, and die attach processes. In such applications, it maybe desirable to have relative consistency regarding the thickness of anadhesive (such as an epoxy layer) between the die backside and thesubstrate. This thickness is sometimes referred to as the “bond linethickness” (i.e., the BLT).

FIG. 4A illustrates bonding machine 400 (e.g., a die attach machine,etc.). Bonding machine 400 includes bond head assembly 402 carrying abonding tool 402 a (e.g., die attach tool 402 a). Bonding tool 402 aincludes a body portion 402 a 1 carrying (e.g., using vacuum, etc.)semiconductor element 404 (e.g., semiconductor die 404). Bonding tool402 a includes a contact surface 402 a 2 for contacting semiconductorelement 404 during a die attach process. Bonding tool 402 a alsoincludes standoff 402 a 3 (e.g., a post or the like) for controlling thez-height/descent during the die attach process. Multiple standoffs maybe included (e.g., see FIG. 2).

Bonding machine 400 also includes a support structure 408 (e.g., a chuckor the like) (where support structure 408 is carried by machine base410). Substrate 406 is supported by support structure 408, and includesadhesive (e.g., a conventional die attach adhesive such as an epoxyadhesive).

FIG. 4B illustrates bond head assembly 402 having descended such thatbonding tool 402 a attaches semiconductor element 404 to substrate 406,with adhesive 406 a disposed therebetween. As shown in FIG. 4B, adhesive406 a has spread out through the die attach process. Standoff 402 a 3controls the height to which bond head assembly 402 (including bondingtool 402 a) descends during the die attach process, thereby controllingthe amount of squash of adhesive 406 a, and hence controlling the bondline thickness (BLT).

Although the invention has been illustrated and described in connectionwith specific example structures and methods, it is not limited thereto.For example, aspects of the invention may relate to one or morestandoffs, having any desired shape and/or configuration. Further, suchstandoffs may be used to define the SOH (or BLT or other criteria) whileupon contact with the substrate—or such standoffs may be used to definethe SOH (or BLT or other criteria) by moving a predetermined distanceaway after contact with the substrate (e.g., see FIG. 3E).

Further still, the machines may vary considerably from the simplifieddrawings provided herein. For example, bonding tools within the scope ofthe invention may also be a pick tool (where the bonding tool “picks” asemiconductor element from a supply, such as a wafer, and the places thesemiconductor element on the substrate). In other examples, the bondingtool may receive the semiconductor element through some type of transferoperation (e.g., where the transfer is made from a separate pick tool,or a separate transfer tool, etc.).

Although the invention is illustrated and described primarily byreference to embodiments including one or more structural standoffs, theinvention is not limited thereto. Different and/or additionaltechnologies (non-contact technologies) may be utilized to accuratelycontrol the heights during the bonding processes. For example, a lasersystem may be utilized to detect a bonding surface and/or bonding tool,to control the final height (e.g., the SOH in FIG. 3E, the BLT height inFIG. 4B, etc.). Other example technologies include hall effect sensors,proximity sensors, position sensors, motion sensors, velocity sensors,capacitive sensors, among others.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A method of operating a bonding machine, the methodcomprising the steps of: (a) carrying a semiconductor element with abonding tool; (b) initiating contact between conductive structures ofthe semiconductor element with corresponding conductive structures of asubstrate; (c) lowering the bonding tool after step (b) such that astandoff of the bonding tool contacts an upper surface of the substrate;and (d) raising the bonding tool after step (c).
 2. The method of claim1 wherein step (c) includes contacting a solder mask layer of thesubstrate with the standoff.
 3. The method of claim 1 wherein step (d)includes raising the bonding tool after step (c) by a predeterminedamount.
 4. The method of claim 1 further comprising the step of at leastpartially melting at least one of (i) conductive structures of thesemiconductor element and (ii) corresponding conductive structures of asubstrate between steps (b) and (c).
 5. The method of claim 4 furthercomprising the step of solidifying the conductive structures of thesemiconductor element and the corresponding conductive structures of asubstrate after step (d).
 6. A method of operating a die attach machine,the method comprising the steps of: (a) carrying a semiconductor elementwith a bonding tool; (b) initiating contact between the semiconductorelement and an adhesive material on a substrate; and (c) lowering thebonding tool after step (b) such that a standoff of the bonding toolcontacts an upper surface of the substrate.